Integrated circuits are continuously undergoing development to provide smaller footprints while providing the same or higher circuit densities. Additionally, the packaging of integrated circuit is also continuously undergoing development to provide packages only slightly larger than the integrated circuits they are housing. For instance, integrated circuit packages using wire bonds connected to a lead frame, that typically require a relatively large footprint, are generally being replaced with chip scale packages (CSP), such as wafer level packages (WLP), wherein the size of the package is substantially the same or slightly larger than the integrated circuit it houses.
In a typical wafer level package (WLP), solder balls are attached to an integrated circuit such that the solder balls are electrically connected to the respective bond pads of the integrated circuit. In one implementation, the solder balls are electrically connected to bond pads by way of only an under bump metallurgy (UBM) layer. This is typically referred to as the bump on pad (BOP) implementation. In another implementation, solder balls are electrically connected to bond pads by way of the UBM layer and a redistribution layer (RDL). The redistribution layer (RDL) allows the pattern of the solder bumps to be different than the pattern of the bond pads of the integrated circuits.
In some packaging configurations, such as in flip chips, the integrated circuit is typically flipped up-side-down so that the solder bumps face downward, and placed on a printed circuit board (PCB). The integrated circuit and PCB are then heated to reflow the solder, thereby electrically attaching the solder balls to electrical contacts on the PCB. The PCB is typically made out of a generally flexible substrate. During manufacturing, handling, and operation, the flexible substrate bends and absorbs much of the forces to which it is subjected. However, the bending of the flexible substrate creates stress around the region where the solder balls attach to the integrated circuit. Sometimes the stress causes permanent damage to the integrated circuit.